s390x/css: disabled subchannels cannot be status pending

The 3270 code will try to post an attention interrupt when the
3270 emulator (e.g. x3270) attaches. If the guest has not yet
enabled the subchannel for the 3270 device, we will present a spurious
cc 1 (status pending) when it uses msch on it later on, e.g. when
trying to enable the subchannel.

To fix this, just don't do anything in css_conditional_io_interrupt()
if the subchannel is not enabled. The 3270 code will work fine with
that, and the other user of this function (virtio-ccw) never
attempts to post an interrupt for a disabled device to begin with.

CC: qemu-stable@nongnu.org
Reported-by: Thomas Huth <thuth@redhat.com>
Tested-by: Thomas Huth <thuth@redhat.com>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Halil Pasic <pasic@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
(cherry picked from commit 6e9c893ecd00afd5344c35d0d0ded50eaa0938f6)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

diff --git a/hw/s390x/css.c b/hw/s390x/css.c
index 301bf1772f554f3778c8841e5729de67a0c27b85..56c3fa8c89b1ad3f326346b59c51825431bf6d7f 100644 (file)
--- a/hw/s390x/css.c
+++ b/hw/s390x/css.c
@@ -616,6 +616,14 @@ void css_inject_io_interrupt(SubchDev *sch)
 
 void css_conditional_io_interrupt(SubchDev *sch)
 {
+    /*
+     * If the subchannel is not enabled, it is not made status pending
+     * (see PoP p. 16-17, "Status Control").
+     */
+    if (!(sch->curr_status.pmcw.flags & PMCW_FLAGS_MASK_ENA)) {
+        return;
+    }
+
     /*
      * If the subchannel is not currently status pending, make it pending
      * with alert status.